From f8d808ed1ba0019997f18ff2be0cf85e33a31022 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Thu, 15 Jun 2023 16:37:51 +1000 Subject: [PATCH] KVM: SVM: Rewrite sev_es_prepare_switch_to_guest()'s comment about swap types Rewrite the comment(s) in sev_es_prepare_switch_to_guest() to explain the swap types employed by the CPU for SEV-ES guests, i.e. to explain why KVM needs to save a seemingly random subset of host state, and to provide a decoder for the APM's Type-A/B/C terminology. Signed-off-by: Alexey Kardashevskiy Link: https://lore.kernel.org/r/20230615063757.3039121-4-aik@amd.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/sev.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index fd6e316c1a23d..d58a25a92aa3f 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -3023,19 +3023,24 @@ void sev_es_vcpu_reset(struct vcpu_svm *svm) void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa) { /* - * As an SEV-ES guest, hardware will restore the host state on VMEXIT, - * of which one step is to perform a VMLOAD. KVM performs the - * corresponding VMSAVE in svm_prepare_guest_switch for both - * traditional and SEV-ES guests. + * All host state for SEV-ES guests is categorized into three swap types + * based on how it is handled by hardware during a world switch: + * + * A: VMRUN: Host state saved in host save area + * VMEXIT: Host state loaded from host save area + * + * B: VMRUN: Host state _NOT_ saved in host save area + * VMEXIT: Host state loaded from host save area + * + * C: VMRUN: Host state _NOT_ saved in host save area + * VMEXIT: Host state initialized to default(reset) values + * + * Manually save type-B state, i.e. state that is loaded by VMEXIT but + * isn't saved by VMRUN, that isn't already saved by VMSAVE (performed + * by common SVM code). */ - - /* XCR0 is restored on VMEXIT, save the current host value */ hostsa->xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK); - - /* PKRU is restored on VMEXIT, save the current host value */ hostsa->pkru = read_pkru(); - - /* MSR_IA32_XSS is restored on VMEXIT, save the currnet host value */ hostsa->xss = host_xss; } -- 2.30.2